Technical Field
The present invention relates generally to the field of implantable repair devices. More particularly, but not exclusively, the present invention concerns medical devices for replacing, repairing and/or regenerating damaged or diseased cartilage, and to manufacturing methods for such devices. The present invention more specifically relates to a device for the replacement, partial replacement or augmentation of damaged articular cartilage including, for example, the articular cartilage of the knee joint, the hip joint, the shoulder joint, finger joints and the ankle joint.
Except where specified below the term ‘fibroin’ is used to refer generically to the main structural protein of cocoon silks whether they are derived from the domesticated Mulberry Silkworm (Bombyx mori) or a transgenic silkworm or from any Wild Silkworm including, but not limited to those producing Muga, Eri or Tussah silks. Furthermore, the term ‘silk’ is used to refer to the natural line fibre that silkworms extrude, which comprises chiefly the two main proteins, sericin and fibroin, fibroin being the structural fibres in the silk, and sericin being the material surrounding the fibroin and sticking the fibres together in the cocoon. ‘Silk cocoon’ or ‘cocoon’ is used to refer to the casing of silk spun by the larvae of the silk worm for protection during the pupal stage.
Description of the Related Art
Cartilage in the adult mammalian body occurs in three principal forms: hyaline cartilage; white fibrocartilage; and yellow elastic cartilage. Hyaline cartilage is chiefly present as articular cartilage in the synovial diarthroidal joints e.g. the knee, hip and shoulder, and between long bones, where it forms the stiff and smooth articulating surfaces. White fibrocartilage is present in the menisci of the knee and temporomandibular joint of the jaw and in intervertebral discs. Yellow elastic cartilage gives support to the epiglottis, Eustachian tube and external car.
Three pathological conditions involving cartilage damage are very common: osteoarthrosis of articular cartilage; injury to the fibrocartilage of the knee menisci; collapse, rupture or herniation of the intervertebral disc; and damage causes by rheumatoid arthritis. Osteoarthrosis is caused by the progressive damage and breakdown of articular cartilage most commonly in the hip and knee and is an important cause of pain and reduced mobility in young and old people alike. Injury to the fibrocartilage of the meniscus is a common sports injury and is also seen as a result of road traffic accidents and other traumatic injuries.
Articular cartilage is highly specialized to provide a relatively frictionless, highly lubricated, wear resistant surface between relatively rigid bones. It also functions to transmit and distribute the forces arising from loaded contact to the surrounding cartilage and underlying subchondral trabecular bone. It is a nonvascular connective tissue largely composed of a fluid phase consisting principally of water and electrolytes interspersed in a solid phase containing type II collagen fibrils, proteo-glycan and other glycoproteins. The latter constituents surround, and are secreted by, highly specialized mesenchymal cells, the chondrocytes, which account for some 10% of the volume of articular cartilage. The collagen fibrils within articular cartilage are arranged in a complex arcade structure forming columns arranged normal to and anchored in the osteochondral junction. These columns run up through the deep layer of cartilage, but the predominant fibre orientation gradually changes to form the arches of the arcade structure in the superficial cartilage. In the superficial layer which abuts the joint space, the meshwork of collagen fibrils is much denser while the fibrils are almost entirely tangential to the cartilage surface. The orientation of collagen in articular cartilage is vital to its mechanical function. Healthy articular cartilage is strong and stiff (modulus between 1 and 20 MPa).
No wholly satisfactory procedure exists for replacing damaged articular cartilage in osteoarthrosis and instead in the case of the two most frequently injured joints, the hip and knee, artificial prostheses are most commonly used to replace the entire joint. While these increase mobility and reduce pain they suffer from progressive wear, mechanical failure, adverse tissue reactions and loosening at their interphase with the bone. Accordingly, there has been much work around the area of providing a suitable implantable repair material with improved performance over the currently available prostheses.
One such device is described in WO 2007/020449 A2, describing a cartilaginous tissue repair device with a biocompatible, bioresorbable three-dimensional silk or other fibre lay and a biocompatible, bioresorbable substantially porous silk-based or other hydrogel partially or substantially filling the interstices of the fibre lay.
International patent application number PCT/IB2009/051775 (published under WO2009/133532 A2) discloses a silk fibroin solution and method that can be used to make an improved fibroin material that has been found to be efficient as an implant for cartilage repair. The method for the preparation of the regenerated silk fibroin solution comprises the steps of: (a) treating the silk or silk with an ionic reagent comprising aqueous solutions of one or more of ammonium hydroxide, ammonium chloride, ammonium bromide, ammonium nitrate, potassium hydroxide, potassium chloride, potassium bromide or potassium nitrate; (b) subsequently drying the silk or silk cocoons after treatment of the silk or silk cocoons with the ionic reagent; and (c) subsequently dissolving the silk or silk cocoons in a chaotropic agent.
Furthermore, International patent application number PCT/GB2009/050727 (published under WO2009/156760 A2) discloses method for the preparation of an implantable material for the repair, augmentation or replacement of bone from a fibroin solution. The method comprises: preparing a gel from fibroin solution; preparing a material by subjecting the gel to one or more steps of freezing and thawing the gel, wherein the step of preparing the gel from the fibroin solution is performed in the presence of phosphate ions. The material is generally treated with calcium ions to form a fibroin-apatite. A further method step comprises the step of treating the material with an isocyanate to form cross-links. The implantable material has been found to be efficient as an implant for bone repair.
It is an object of the present invention to provide an implantable repair device capable of load bearing and with improved or enhanced abilities to integrate with existing bone or cartilage. It is another object of the present invention to provide an implantable repair device adapted to provide improved articulation of the joint following cartilage replacement. It is a further object of the invention to provide a device with a relatively frictionless, highly lubricated, wear resistant surface that minimises damage to juxtaposed tissues and which is as close to the capabilities of articular cartilage as is possible.